As banks blame new consumer debit card fee proposals on U.S. Sen. Dick Durbin's effort to limit swipe charges on retail businesses, the No. 2 Senate Democrat pushed back Wednesday, pressing Wells Fargo to explain its proposal to charge customers to make up the lost revenue.

Durbin of Illinois, the Senate's majority whip, called the bank out on its claim that they have to impose the new fees on customers because of his amendment to the Dodd-Frank financial reform law that nearly cut in half the average amount banks charge retail businesses each time a customers pays with a debit card, to 24 cents per transaction from 44 cents.

The fees stores pay are called interchange or swipe fees, which Visa and MasterCard set uniformly for banks. Under Dodd-Frank, the Federal Reserve, which estimated that processing debit transactions range from four to 12 cents, can limit these fees.

Durbin questioned Wells Fargo's reasoning for imposing a $3 monthly debit card fee on customers in five test states when the California financial services company reported a record 21 percent increase in earnings in its latest quarterly filing.

"Instead of making up costs, your new consumer fee appears to be a plain attempt to increase your profits-even though your bank just reported third quarter profits that hit a record high," Durbin said in a letter to Wells Fargo & Company CEO John G. Stumpf.

Durbin noted that Wells Fargo has not made publicly available its cost or revenue data on debit transactions. Using data from an April industry report, Wells Fargo made in 2010 an estimated $2.2 billion on swipe fees from more than 5 million transactions with Wells Fargo debit cards in 2010.

Under the Fed's new rule, Durbin estimates that the revenue would go down to about $1.2 billion.

Debit Card Fee Club: Wells Fargo, Bank America, JP Morgan Chase, and Others

"Your spokesperson's claim that Wells Fargo needs to charge all its customers an additional monthly fee of more than $3 in order to make up the 'cost' of providing debit cards simply does not add up," he wrote.

Other banks are rolling out new debit card fees too. Bank of America on Sept. 30 announced plans to institute a $5 fee for each month a debit card is used. Chase is also testing out a $3 fee.

A group of Democrats in the U.S. House of Representatives last week asked Attorney General Eric Holder to investigate potential collusion among banks, due to statements made from financial institutions and trade associations about imposing new fees in response to the Dodd-Frank reforms.

A Wells Fargo representative did not return a request for comment.

Durbin Letter Oct. 19 2011